1. Technical Field
The invention relates to vibration damping devices which develop damping performance when being applied to a suspension member, such as for automobiles or other equipment. More particularly, the invention relates to such a damping device using an electrorheological (ER) fluid as the damping medium, which device is of a relatively simple structure, easy to assemble and to apply a voltage to the ER fluid contained therein for changing the damping characteristics of the device. Even more particularly, the invention relates to an ER damper in which one or both of the electrodes have a splined or fluted configuration.
2. Background Information
Vibration damping devices have been used for considerable periods of time to dampen the vibrational forces applied to the suspension system of vehicles to provide a smoother ride by reducing the vibrations caused by road bumps and depressions passing from the tires to the vehicle frame by the interposing of oil-filled shock absorbers or high-pressure gas damping devices.
Although these prior art oil and high-pressure gas damping devices have proven satisfactory, a more recent development has evolved in which an electrorheological or electroviscous fluid is used within the chamber of the damping device, wherein the liquid is in contact with one or more electrodes, usually mounted in a restrictive passage, which depending upon the size of the electrodes and the amount of voltage applied to the liquid, will change the viscosity of the liquid, enabling the damping device to have a greater range of damping characteristics than those achieved by the high-pressure gas or oil-filled shock absorbers.
An example of an anti-vibration device which uses an expandable liquid chamber containing an electrorheological fluid is shown in U.S. Pat. No. 4,973,031. U.S. Pat. No. 4,858,733 discloses another damping device using electrodes in combination with an electroviscous liquid contained within closed chambers. The liquid is movable through a restricted passage where voltage is applied to the electroviscous liquid as it moves through the passage to change its viscosity to achieve various damping effects. Various other types of such ER vibration damping devices use elastomeric members or sleeves for containing the ER fluid, such as shown in U.S. Pat. No. 5,180,145. Although these devices have proved satisfactory, they are limited as to the amount of internal pressures available for damping, since the sleeves expand and affect the response time.
Therefore, the use of rigid fluid chambers formed of metal have been utilized with ER fluids in order to be able to develop higher internal pressure and quicker response times. U.S. Pat. Nos. 4,819,772 and 5,259,487 are believed to be the closest prior art to the vibration damping device of the present invention. The damping devices of both of these patents use an ER fluid which is contained within rigid housings to provide for increased pressures and quicker response time not believed obtainable with ER dampers using an elastomeric sleeve or bellows for the chamber-forming member.
However, the structures of both of these prior art damping devices require a complicated structure consisting of numerous parts in order to achieve the electrical isolation required for applying a voltage to the restricted orifices or ducts through which the ER fluid moves, and requires the passage of the wires applying the voltage to the electrode to pass through the ER fluid chamber. Likewise, the outer body or housing must be of a rigid metal, since this outer housing is connected at one end directly to one of the spaced vehicle components, and therefore must be of sufficient strength to support the various loads and forces applied thereto. An outer end of the piston rod is connected to the other of the spaced vehicle components for mounting the vibration damping device on the vehicle.
Another problem that can exist in dampers using ER fluids is that the constricted areas adjacent the electrodes can cause a high shear-rate in the restricted flow channel, thereby decreasing the difference between field-on and field-off damping force values provided by the ER effect. Some of these problems are eliminated by the providing of bleed holes or check valves in the piston.
Thus, the need exists for an improved vibration damping device using ER fluids which is of a simpler construction, which is able to withstand the various loads and forces exerted thereon when mounted between spaced structural components of a vehicle, and which enables a voltage to be applied to the electrode contained within the damping device in an easier manner than existing ER fluid dampers, and which reduces the high shear-rate in the flow channel.